FORECAST FORKA MEASURE OF FORECAST INSTABILITY
FF

Forecast Fork

Is the forecast stable, or forking?
A measure of forecast instability

Is the forecast stable,
or forking?

Most weather products tell you the forecast. Forecast Fork tells you whether to trust it — how much the ensembles disagree, which competing scenarios are still unresolved, and how likely the forecast is to change in the next few cycles. Publicly, and continuously verified.

See it live → Peril watch

The idea

A forecast can be confident — every model and member converging on one outcome — or forked: split into distinct scenarios the atmosphere hasn't chosen between yet. The second kind busts. Forecast Fork is the probability that materially distinct scenarios remain unresolved — and, uniquely, that the forecast itself is about to move.

FFI = P( materially distinct forecast scenarios remain unresolved )  ·  from cluster divergence, spread growth, cross-model disagreement, run-to-run momentum & bimodality

The components

Enginecalibrated blend

A multi-model ensemble blend (full-physics + AI) with per-region, per-lead skill weighting and honest, recalibrated probabilities.

Indexthe fork number

One number per region & lead: how forked the forecast is — the probability it stays unresolved or revises.

Scenariospersistent regimes

The competing weather patterns tracked cycle to cycle — when a scenario appears, gains support, splits, or wins.

Momentumrun-to-run

How the distribution is moving between cycles: drift, spread acceleration, cluster-mass velocity, reversals.

Confidencecalibrated stability

A validated, reliability-checked estimate of how much to trust the current forecast — not just its central value.

Archiveissue-time record

An immutable, provenance-stamped record of every forecast as it was issued, linked to what actually happened.

Why it's different

Not "will it be hot"

  • the full outcome distribution, not a single number
  • the competing scenarios, named and tracked
  • whether the forecast is likely to change
  • where and when the models will most likely bust

Public & provable

  • continuously, out-of-sample verified — in the open
  • model-by-model reliability and error, published
  • honest probabilities (recalibrated, validated)
  • a recognizable measure anyone can cite

Forecast Fork is the transparent, auditable layer of Weather Trader — a prediction market for the atmosphere. The maps and verification are free and public; the goal is for "the Forecast Fork is high" to become how people say a forecast is unsettled.